1.Field of the Invention
The present invention relates to a process for passivating metal surfaces to enhance the stability of gaseous hydride mixtures at low concentration in contact therewith.
2. Description of the Background
In the electronics industry, and in view of environmental considerations, there is an important need for stable gas mixtures containing low concentrations of gaseous hydrides in the ppb to ppm range. The standard practice in industry is to prepare such mixtures in compressed gas cylinders, in which such mixtures are often stored for extended periods of time. However, due to reactions between gas mixtures containing such amounts of gaseous hydrides and the metal surfaces of containers containing these mixtures, it is very difficult to stabilize the same.
One approach to overcoming this instability and to maintaining a constant gas mixture concentration is to minimize the contact time between the low concentration hydrides and metal containers by storing a high concentration mixture in the cylinder and then diluting immediately before use. Unfortunately, however, in many instances, it is desirable, if not necessary, to store the gas mixtures in metal cylinders for extended periods of time.
Another approach for maintaining a constant gas mixture concentration of low concentration hydrides is saturation passivation. In this technique, the container is subjected to several cycles of evacuating and filling with a much higher concentration of the same gaseous hydride, prior to being filled with the low concentration hydride mixture of interest. This procedure is repeated several times based upon previous empirical studies. This technique is of limited usefulness, however, as a higher concentration of the same hydride must be used for conditioning the container, and it is very disadvantageous to handle large amounts of toxic gases, such as arsine, during the process.
Thus, a need continues to exist for a passivation process which is suitable for stabilizing gaseous hydride mixtures, which avoids the drawbacks of the conventional approaches described above.